Netgear D6200 User Manual download pdf (Page 117)

Advanced Settings

117

D6200 WiFi DSL Modem Router

source address and port, and sends this request message through the Internet to the IRC

server.

4. Noting your port triggering rule and having observed the destination port number of 6667,

your WiFi DSL modem router creates an additional session entry to send any incoming port

113 traffic to your computer.

5. The IRC server sends a return message to your WiFi DSL modem router using the

NAT-assigned source port (as in the previous example, say port 33333) as the destination

port. The IRC server also sends an identify message to your WiFi DSL modem router with

destination port 113.

6. Upon receiving the incoming message to destination port 33333, your WiFi DSL modem

router checks its session table to determine whether an active session for port number

33333 exists. Finding an active session, the WiFi DSL modem router restores the original

address information replaced by NAT and sends this reply message to your computer.

7. Upon receiving the incoming message to destination port 113, your WiFi DSL modem

router checks its session table and learns that an active session exists for port 113

associated with your computer. The WiFi DSL modem router replaces the message’s

destination IP address with your computer’s IP address and forwards the message to your

computer.

8. When you finish your chat session, your WiFi DSL modem router eventually senses a

period of inactivity in the communications. The WiFi DSL modem router then removes the

session information from its session table, and incoming traffic is no longer accepted on port

numbers 33333 or 113.

To configure port triggering, you need to know which inbound ports the application needs.

Also, you need to know the number of the outbound port that triggers the opening of the

inbound ports. You can usually determine this information by contacting the publisher of the

application or user groups or newsgroups.

Note: Only one computer at a time can use the triggered application.

Port Forwarding to Permit External Host Communications

In both of the preceding examples, your computer initiates an application session with a

server computer on the Internet. However, you might need to allow a client computer on the

Internet to initiate a connection to a server computer on your network. Normally, your WiFi

DSL modem router ignores any inbound traffic that is not a response to your own outbound

traffic. You can configure exceptions to this default rule by using the port forwarding feature.

A typical application of port forwarding can be shown by reversing the client-server

relationship from the previous web server example. In this case, a remote computer’s

browser needs to access a web server running on a computer in your local network. Using

port forwarding, you can tell the WiFi DSL modem router, “When you receive incoming traffic

on port 80 (the standard port number for a web server process), forward it to the local

computer at 192.168.1.123.” The following sequence shows the effects of the port forwarding

rule you have defined:

1 2 ... 112 113 114 115 116 117 118 119 120 121 122 ... 161 162

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Netgear D6200 User Manual Page 117

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